The first part just means they need to have rubber padding. Still expensive since the design it's a one time job and can be reused for trains, trams, buses etc.
It's not that simple. Something different is required depending how the doors close (pneumatic, electric) and the expected use (high / low speed, crowded or not).
If the padding is too squashy, a trapped hand won't be detected and the person could be dragged under the train. Too sensitive, and someone leaning a suitcase on the door prevents the train from leaving.
If the padding is too squashy, a trapped hand won't be detected and the person could be dragged under the train. Too sensitive, and someone leaning a suitcase on the door prevents the train from leaving.